Question

1. a student attempts to identify an unknown compound by using chemical reactions to calculate mass relationships. after heating a sample weighing 0.4510 g, the mass decreased to 0.4467 g. when the product was reacted to form a chloride, the resulting mass was 0.4780 g.

a. is this unknown a carbonate or hydrogen carbonate? state you reasoning.
b. given the answer to part a, the unknown is one of what two compounds?
__ or __
c. write the overall balanced chemical equations for the reaction of each possible unknown (part b) with hcl.
d. given the stoichiometry of the equation in (c), how many moles of the chloride salt would be produced from one mole of the original unknown compound?

Explanation:

Step1: Analyze mass - loss on heating

When a hydrogen carbonate is heated, it decomposes to form a carbonate, water, and carbon dioxide, resulting in a mass - loss. Carbonates do not decompose on heating under normal conditions in this context. The mass of the sample decreased from 0.4510 g to 0.4467 g upon heating, indicating a decomposition reaction characteristic of a hydrogen carbonate.

Step2: Identify possible compounds

If it is a hydrogen carbonate, common hydrogen carbonates are sodium hydrogen carbonate ($NaHCO_3$) and potassium hydrogen carbonate ($KHCO_3$).

Step3: Write chemical equations

For $NaHCO_3$:
\[NaHCO_3+HCl = NaCl + H_2O+CO_2\uparrow\]
For $KHCO_3$:
\[KHCO_3 + HCl=KCl + H_2O + CO_2\uparrow\]

Step4: Determine moles of chloride salt

From the balanced chemical equations, for both $NaHCO_3$ and $KHCO_3$, 1 mole of the original hydrogen - carbonate compound reacts with 1 mole of HCl to produce 1 mole of the corresponding chloride salt (NaCl or KCl).

Answer:

a. It is a hydrogen carbonate because there is a mass - loss on heating, which is characteristic of the decomposition of a hydrogen carbonate to a carbonate, water, and carbon dioxide.
b. Sodium hydrogen carbonate ($NaHCO_3$) or potassium hydrogen carbonate ($KHCO_3$)
c. $NaHCO_3+HCl = NaCl + H_2O+CO_2\uparrow$; $KHCO_3 + HCl=KCl + H_2O + CO_2\uparrow$
d. 1 mole